Determination of ultrasonic parameters such as sound velocity and attenuation in engineering materials and many biological tissues have been well-documented in literature, e.g., "Physical Principles of Ultrasonic Diagnosis" by P. N. T. Wells, (Academic Press, New York, 1969). Sound end particularly ultrasonia sound have been used in numerous devices to determine various physical characteristics of materials, but these Known devices do not relate to a method for determining the ripeness or maturity of fruits end/or vegetables. For example, U.S. Pat. Nos. 2,966,057 and 2,538,444 disclose systems that measure attenuation of ultrasonic energy when it passes through a medium. Despite the wide use and success of these methods in industry and medicine, very little has been done to employ this technique for testing fresh food produce.
The main problems associated with the application of this technique are:
a) Fruit tissue is an inhomogeneous material. PA1 b) Fruit tissue is a highly-attenuative material for high frequency ultrasonic signals. PA1 c) Measuring time end detection of wave velocity and internal defects is difficult at low frequencies.
Mizrach et al. (Mizrach, A., N. Galili, and G. Rosenhouse, 1989. Determination of fruit and vegetable properties by ultrasonic excitation. Transaction of the ASAE, 32(6): 2053-2058. Mizrach, A., Galili, G. Rosenhouse, and D. C. Teitel, 1991. Acoustical, mechanical and quality parameters of winter grown melon tissue. Transactions of ASAE, 34(5):2135-2138. Mizrach, A., N. Galili, and G. Rosenhouse, 1992, Half-cut fruit response to ultrasonic excitation. ASAE Paper No. 923017. American Society of Agricultural Engineers, St. Joseph, Mich.) revising previous work, evaluated the use of low-frequency ultrasonic excitation for the determining the quality of fruit tissue and concluded that ultrasonic testing is a potential technique for the non-hazardous measurement of internal quality and latent defects in fruits and vegetables.
However, none of these previously proposed techniques are suitable for non-destructive, whole-fruit testing. In many kinds of fruits, the attenuation of sound prevents it from passing through the entire fruit. Hence, local ultrasonic tests over the peel of the fruit were performed experimentally, assuming that the internal fruit tissue next to the peel, effects the peel response.
Preliminary investigation on local testing of ultrasonic surface waves in the peel of a whole fruit was performed by the inventors. It was found that the acoustical parameters of some whole-fruits related to the ripening process and the changes in the mechanical and quality parameters of the fruit flesh.